JP3239709B2 - Acceleration sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor, and more particularly, to an acceleration sensor using a piezoelectric element used in, for example, a car navigation system.

[0002]

2. Description of the Related Art FIG. 10 is an illustrative view showing one example of a conventional acceleration sensor. The acceleration sensor 1 includes a substrate 2. The piezoelectric element 3 is formed on one surface of the substrate 2. Substrate 2
Is fixed, and a weight 4 is attached to the other end of the substrate 2. In the acceleration sensor 1, when acceleration is applied, a force is applied to the weight 4, and the substrate 2 bends. The piezoelectric element 3 also bends in accordance with the bending of the substrate 2, and charges are generated in the piezoelectric element 3 in accordance with the bending. The polarity of the electric charge generated in the piezoelectric element 3 is reversed depending on the direction of the bending of the substrate 2. Therefore, if the output voltage of the piezoelectric element 3 is measured, the magnitude of the acceleration can be known from the magnitude of the voltage, and the direction of the acceleration can be known from the polarity.

Further, as shown in FIG. 11, both ends of the substrate 2 may be supported. In this acceleration sensor 1, a weight 4 is attached to the center of the substrate 2. Further, piezoelectric elements 3a, 3b, 3c, 3d are formed on both sides of the weight 4. In this acceleration sensor 1, the piezoelectric elements 3a, 3b
And the piezoelectric elements 3c and 3d are polarized in directions opposite to each other. That is, when the piezoelectric elements 3a and 3b are polarized from the outside toward the substrate 2, the piezoelectric element 3a
c and 3d are polarized outward from the substrate 2 side. Therefore, when the same drive signal is given to the piezoelectric elements 3a to 3d, the piezoelectric elements 3a and 3b and the piezoelectric elements 3c and 3d
And the reverse displacement. Therefore, the substrate 2 oscillates in opposite directions on both sides of the weight 4. That is, when the substrate 2 extends on one side of the weight 4, the substrate 2 contracts on the other side of the weight 4. Conversely, when the substrate 2 contracts on one side of the weight 4, the substrate 2 expands on the other side of the weight 4. Therefore, substrate 2
Oscillates in length with its total length unchanged.

Further, for example, opposing piezoelectric elements 3c,
3d is connected to the differential circuit. Since the piezoelectric elements 3c and 3d are polarized outward from the substrate 2, the same signals are output from the piezoelectric elements 3c and 3d when no acceleration is applied. At this time, no signal is output from the differential circuit. When acceleration is applied to the acceleration sensor 1, a force is applied to the weight 4 and the substrate 2 is warped. for that reason,
A signal corresponding to the warpage of the substrate 2 is output from the piezoelectric elements 3c and 3d. However, since both the piezoelectric elements 3c and 3d are polarized outward from the substrate 2 side, the bending state in the polarization direction is reversed, and the piezoelectric elements 3c and 3d are polarized.
Output a different signal. Therefore, an output signal corresponding to the acceleration can be obtained from the differential circuit.

[0005]

In these acceleration sensors, when the ambient temperature changes, the substrate is curved due to the difference in the coefficient of thermal expansion between the substrate and the piezoelectric element. As a result, charge is generated in the piezoelectric element, but it is not possible to distinguish whether the generated charge is due to acceleration or temperature change. For this reason, there is a risk that an erroneous detection may be made as if acceleration is applied even though acceleration is not applied.

Further, in the acceleration sensor shown in FIG. 11, since both ends of the substrate are supported, the displacement of the substrate due to acceleration cannot be increased. Therefore, there is a problem that the output signal of the piezoelectric element is small and the sensitivity is low.

SUMMARY OF THE INVENTION Therefore, a main object of the present invention is to provide an acceleration sensor having high acceleration detection sensitivity and capable of reducing the influence of a signal accompanying a change in ambient temperature.

[0008]

SUMMARY OF THE INVENTION The present invention relates to
A plate-shaped substrate having a surface on which a plurality of piezoelectric elements are formed ,
Two connecting means made of a rigid material extending from both ends in the longitudinal direction of the surface on which the plurality of piezoelectric elements of the substrate are formed, and attached to both extending ends of the two connecting means.
The weight includes one weight, and the weight is formed by a plurality of piezoelectric elements on the substrate.
This is an acceleration sensor in which the center of gravity is arranged on a line orthogonal to the substrate at the center of the formed surface. In this acceleration sensor, a plurality of piezoelectric elements are formed by a plurality of piezoelectric elements on a substrate.
And across the longitudinal center plane is formed on both sides, connecting the hand
Two connecting rods as steps are formed by multiple piezoelectric elements on the substrate
It is formed so as to extend toward the weight from both ends in the longitudinal direction of the formed surface. Further, the plurality of piezoelectric elements a plurality of substrates
The piezoelectric element is formed on both sides of the central portion in the longitudinal direction of the surface on which the piezoelectric element is formed , and the connecting means is formed by bending both sides in the longitudinal direction of the substrate. A weight may be attached to the vehicle. Further, the substrate is bent so that both ends in the longitudinal direction is opposed on one plane, by Rukoto plurality of piezoelectric elements are respectively formed on one surface <br/> on both sides of the opposing portion of the substrate, one plane Pair on
The opposite ends are surfaces on which a plurality of piezoelectric elements are formed,
Portions other than both ends of the substrate may serve as connecting means, and the weight may be attached to the center of the substrate.

When acceleration is applied in the longitudinal direction of the substrate,
The force is applied to the weight, thereby displacing the weight. At this time, one end of the surface of the substrate on which the piezoelectric element is formed is pushed by the connecting means, and the other end is pulled. Therefore, one end side and the other end side of the substrate on which the piezoelectric element is formed,
Displace in opposite directions.

When the ambient temperature changes, the substrate bends due to the difference in thermal expansion coefficient between the substrate and the piezoelectric element. At this time, since the plurality of piezoelectric elements are formed on one surface side of the substrate, the substrate always bends in a certain direction.
That is, one end and the other end of the surface of the substrate on which the piezoelectric element is formed are bent so as to be displaced in the same direction. Therefore, the bending state of the substrate due to the acceleration and the bending state of the substrate due to the change in the ambient temperature are different, and the relationship between the output signals of the plurality of piezoelectric elements is also different. From the relationship between these output signals,
The signal due to the change in the ambient temperature is canceled, and only the signal corresponding to the acceleration can be obtained.

[0011]

According to the present invention, the bending state of the substrate can be made different between when the acceleration is applied and when the ambient temperature changes. If the bending state of the substrate is different, the signal obtained from the piezoelectric element is also different, and only the signal due to the change in ambient temperature can be canceled. Therefore, only the signal corresponding to the acceleration can be obtained, and the detection error can be reduced.

The above objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

[0013]

FIG. 1 is a perspective view showing an example of an acceleration sensor according to the present invention, and FIG. 2 is a sectional view thereof. The acceleration sensor 10 includes a rectangular plate-shaped substrate 12. Substrate 1
Two piezoelectric elements 14a and 14b are formed on one surface of the two. These piezoelectric elements 14a and 14b are
2 are formed on both sides of the central portion in the longitudinal direction. Piezoelectric element 1
4a includes a piezoelectric layer 16a formed of, for example, a piezoelectric ceramic. Electrodes 18 are provided on both sides of the piezoelectric layer 16a.
a, 20a are formed. Then, one electrode 20a
Is adhered to the substrate 12. Similarly, the piezoelectric element 14b includes a piezoelectric layer 16b, and electrodes 18b and 20b are formed on both surfaces thereof. Then, one electrode 20b is bonded to the substrate 12. In these piezoelectric elements 14a and 14b, the piezoelectric layers 16a and 16b are polarized in the same direction. That is, the piezoelectric layers 16a and 16b are polarized, for example, from the outside toward the substrate 12 side.

At both ends in the longitudinal direction of the substrate 12, connecting rods 22 as connecting means are attached. The connecting rod 22
It is formed of a rigid material. The two connecting rods 22 are formed to have the same length, and are connected to the weight 24 on the other side of the substrate 12. Therefore, the weight 24 is disposed on a line orthogonal to the substrate 12 at the center of the substrate 12. In FIG. 1, a triangle indicates a support. That is, the substrate 12
Are supported on both sides of the substrate 12 at the center in the longitudinal direction. Further, the two piezoelectric elements 14a and 14b are connected to a differential circuit.

In the acceleration sensor 10, when an acceleration is applied in the longitudinal direction of the substrate 12, a force acts on the weight 24, which causes the weight 24 to be displaced. Therefore, FIG.
1, one end of the substrate 12 is pushed by the connecting rod 22 and the other end is pulled by the connecting rod 22. Therefore, both ends of the substrate 12 are displaced in directions opposite to each other. Thereby, the piezoelectric elements 14a and 14b also bend in directions opposite to each other. Piezoelectric layer 1 of piezoelectric elements 14a and 14b
Since 6a and 16b are polarized in the same direction, when they are bent in opposite directions, charges of opposite polarity are generated. Therefore, a large output signal corresponding to the acceleration can be obtained from the differential circuit.

When the ambient temperature changes, the substrate 1
2 and the piezoelectric elements 14a and 14b have different coefficients of thermal expansion, so that the substrate 12 is curved. At this time, the piezoelectric elements 14a,
Since the portion 14b is formed on one surface of the substrate 12, the portions where the piezoelectric elements 14a and 14b are formed bend in the same direction. That is, as shown by the solid line in FIG.
The substrate 12 bends in the direction of the piezoelectric elements 14a, 14b, or as indicated by the dashed line, the piezoelectric elements 14a, 1b.
4b. In the structure of the acceleration sensor 10, a bent state as shown in FIG. 3 does not occur due to a change in the ambient temperature. Therefore, the piezoelectric element 14
The charges generated at the terminals a and b have the same polarity, and the output signals of the piezoelectric elements 14a and 14b are canceled by the differential circuit.

As described above, in this acceleration sensor 10,
The signal generated by the change in the ambient temperature is canceled, and only the signal corresponding to the acceleration can be obtained. Therefore, even when the acceleration sensor 10 is used in a place where there is a temperature change, the acceleration can be accurately detected. Moreover, since the substrate 12 is supported at the center, the bending of the substrate 12 is not hindered as in the case of supporting both ends, and both ends of the substrate 12 can be largely displaced. Therefore, the piezoelectric element 1
A large output signal can be obtained from 4a and 14b, and acceleration detection sensitivity can be improved.

As shown in FIG. 5, such an acceleration sensor 10 may be a connecting means by bending both ends of the substrate 12. In this acceleration sensor 10, the substrate 12
Are sharply bent at both ends. Then, triangular weights 24 are attached to the bent both ends of the substrate 12. In this case, the weights 24 are attached to both ends of the substrate 12 by, for example, welding. Of course, the weight 24 may be attached using an adhesive or the like. Even in such an acceleration sensor 10, output signals from the piezoelectric elements 14a and 14b due to a change in ambient temperature can be canceled out in a manner similar to the acceleration sensor shown in FIG.

Further, as shown in FIG.
A weight 24 having substantially the same length as the surface of the substrate 12 on which the a and b are formed may be used. In this case, both ends of the substrate 12 are bent so as to be substantially perpendicular to the surface on which the piezoelectric elements 14a and 14b are formed. As described above, the shape of the weight 24 can be arbitrarily changed, but the piezoelectric element 14
The weight 24 is arranged so that the center of gravity of the weight 24 exists on a line orthogonal to the substrate 12 at the center of the surface where the a and b are formed.

Further, as shown in FIG. 7, the substrate 12 may be bent at three places including the central part in the longitudinal direction, and may be joined so that both ends of the substrate 12 face each other. In the acceleration sensor 10, a weight 24 is attached to a central portion of the substrate 12, that is, a bent portion. The piezoelectric elements 14 are provided on both sides of both ends of the butted substrate 12.
a, 14b are formed. Therefore, the piezoelectric element 14
The portion of the substrate 12 between the surface of the substrate 12 on which a and 14b are formed and the mounting portion of the weight 24 is used as connecting means. In this acceleration sensor 10, both ends of the substrate 12 are supported at both ends of the butted substrate 12. That is, between the piezoelectric elements 14a and 14b,
The substrate 12 is supported. This acceleration sensor 10 is also shown in FIG.
As in the case of the acceleration sensor shown in FIG. 7, the output signals from the piezoelectric elements 14a and 14b due to the change in the ambient temperature can be canceled.

Further, as shown in FIG. 8, the surface of the substrate 12 on which the piezoelectric elements 14a and 14b are formed may be formed so as to face in the width direction. This acceleration sensor 1
0, for example, as shown in FIG.
0 is used. The plate member 30 is formed such that both end sides are half the width of the intermediate portion. These parts are
The plate 30 is formed on one side and the other side in the width direction.
The substrate 12 is formed by bending the plate member 30. At this time, the plate 30 is bent such that both ends of the plate 30 overlap in the width direction.

In this acceleration sensor 10, both ends of the substrate 12 are supported. Then, on the opposing portion of the substrate 12,
The piezoelectric elements 14a and 14b are formed. In this case, the piezoelectric elements 14a and 14b can be made longer than those of the acceleration sensors described above. Moreover, since both ends of the substrate 12 are supported, when acceleration is applied, the portion of the substrate 12 where the piezoelectric elements 14a and 14b are formed is greatly deformed. Thereby, the deformation of the piezoelectric elements 14a and 14b can be increased, and a large output signal can be obtained. Therefore, the acceleration detection sensitivity can be improved.

In the acceleration sensor 10 described above, the acceleration is detected by measuring the output voltages of the piezoelectric elements 14a and 14b. However, an excitation circuit may be connected to the piezoelectric elements 14a and 14b for excitation. In this case, the piezoelectric element 14
Due to the deformation of a and 14b, for example, the resonance frequency and the impedance change. Therefore, the acceleration can be detected from a change in the frequency or a change in the impedance of the signal output from the piezoelectric elements 14a and 14b. Also in this case, since the deformation of the piezoelectric elements 14a and 14b due to the change in the ambient temperature is the same, the resonance frequency and the impedance change similarly. Therefore, the change in the resonance frequency and the change in the impedance of the piezoelectric elements 14a and 14b can be canceled out, and the influence of the temperature change can be reduced.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of an acceleration sensor according to the present invention.

FIG. 2 is a sectional view of the acceleration sensor shown in FIG.

FIG. 3 is an illustrative view showing a state when acceleration is applied to the acceleration sensor shown in FIG. 1;

FIG. 4 is an illustrative view showing a state when the acceleration sensor shown in FIG. 1 is deformed by a temperature change;

FIG. 5 is a perspective view showing another example of the acceleration sensor of the present invention.

FIG. 6 is a perspective view showing still another example of the acceleration sensor of the present invention.

FIG. 7 is a perspective view showing another example of the acceleration sensor of the present invention.

FIG. 8 is a perspective view showing still another example of the acceleration sensor of the present invention.

FIG. 9 is a plan view showing a plate material for manufacturing a substrate used for the acceleration sensor shown in FIG.

FIG. 10 is an illustrative view showing one example of a conventional acceleration sensor.

FIG. 11 is an illustrative view showing another example of the conventional acceleration sensor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Acceleration sensor 12 Substrate 14a 14b Piezoelectric element 22 Connecting rod 24 Weight

Claims (4)

(57) [Claims] 1. A plurality of piezoelectric elements are formed on one surface.
Plate-like substrate having a surface, the length of the surface of the substrate on which the plurality of piezoelectric elements are formed
Two connecting means formed of a rigid material extending from opposite ends, and one weight attached to the extending end of both of the two connecting means , wherein the plurality of piezoelectric elements of the substrate are An acceleration sensor, wherein a center of gravity is arranged on a line orthogonal to the substrate at a center of the formed surface. Wherein said plurality of piezoelectric elements are the double of the substrate
Across the longitudinal center of the surface on which the number of piezoelectric elements are formed is formed on <br/> both sides, the two connecting rods of the said coupling means the double of the substrate
The acceleration sensor according to claim 1, wherein the acceleration sensor is formed so as to extend toward the weight from both ends in the longitudinal direction of the surface on which the number of piezoelectric elements is formed . Wherein said plurality of piezoelectric elements are the double of the substrate
Sandwich the center in the longitudinal direction of the surface on which
In is formed on both sides, the coupling means are formed by bending both sides in the longitudinal direction of the substrate, the weight at both ends of the substrate which is the connecting means is attached, the acceleration sensor according to claim 1 . Wherein said substrate opposite ends in the longitudinal direction are bent so as to face in one plane, by Rukoto said plurality of piezoelectric elements are respectively formed on one surface of both sides of the opposing portion of the substrate, wherein Opposite ends on one plane
2. A surface on which a plurality of piezoelectric elements are formed, a portion excluding both ends of the substrate serves as the connecting means, and the weight is attached to a central portion of the substrate.
2. The acceleration sensor according to 1.